1. Field of the Invention
The present invention relates to a head mounted display including an eyeglasses frame-like frame to be mounted onto an observer's head and image display devices.
2. Description of the Related Art
A virtual image display device (image display device) for permitting a two-dimensional image formed by an image forming device to be observed by an observer (viewer) as a magnified virtual image through a virtual image optical system has been known, for example from Japanese Patent Laid-open No. 2006-162767 (hereinafter referred to as Patent Document 1).
As illustrated by a conceptual diagram shown in FIG. 8, this image display device 100 includes an image forming device 111 having a plurality of pixels arranged in a two-dimensional matrix, a collimating optical system 112 by which beams emitted from pixels of the image forming device 111 are turned into parallel beams, and light guide means (optical device) 120 on which the parallel beams obtained through the collimating optical system 112 are incident, through which the parallel beams are guided and from which the beams are emitted. Incidentally, the image generating device 110 includes the image forming device 111 and the collimating optical system 112. The light guide means 120 includes a light guide plate 121 for propagating incident beams through the inside thereof by total reflections and emitting the beams therefrom, first deflecting means 130 (including, for example, a monolayer light-reflective film) for reflecting the beams entering the light guide plate 121 so that the beams entering the light guide plate 121 undergo total reflections in the inside of the light guide plate 121, and second deflecting means 140 (including, for example, a light-reflective multilayer film having a multilayer laminated structure) by which the beams propagated through the inside of the light guide plate 121 while undergoing total reflections are emitted from the light guide plate 121.
Or, a virtual image display device (image display device) in which a holographic diffraction grating is used for permitting a two-dimensional image formed by an image forming device to be observed by an observer as a magnified virtual image through a virtual image optical system has been known, for example from Japanese Patent Laid-open No. 2007-94175 (hereinafter referred to as Patent Document 2).
As illustrated by a conceptual diagram shown in FIG. 10A, this image display device 300 basically includes an image forming device 111 operable to display an image, a collimating optical system 112, and light guide means (optical device) 320 on which beams displayed on the image forming device 111 are incident and through which the image is guided to an observer's pupil 41. Here, the light guide means 320 includes a light guide plate 321, and a first diffraction grating member 330 and a second diffraction grating member 340 each of which is provided on the light guide plate 321 and includes a reflection-type volume holographic diffraction grating. Beams emitted from pixels of the image forming device 111 are incident on the collimating optical system 112, parallel beams are produced by the collimating optical system 112, and the parallel beams are incident on the light guide plate 321. The parallel beams enter the light guide plate 321 through a first surface 322, and are emitted from the light guide plate 321 through the first surface 322. On the other hand, the first diffraction grating member 330 and the second diffraction grating member 340 are mounted to a second surface 323 of the light guide plate 321, the second surface 323 being parallel to the first surface 322 of the light guide plate 321.
The image display device including the image generating device 110 and the light guide means 120, 320 is mounted to a frame 1010 resembling a frame of a pair of eyeglasses. Specifically, as for example shown in FIG. 1 of Patent Document 1, two image generating devices 110 are fixed to both end portions of a front portion 1011 of the eyeglasses frame-like frame 1010 through fixing members 1017, respectively (see FIG. 30).